Adhesive compositions based on styrenic block copolymers as thermoplastic elastomer components are well known in the art. These compositions are for instance used in pressure sensitive adhesive (PSA) for industrial tapes, packaging tapes, labels and bandages (e.g. plasters).
More in particular styrene-isoprene-styrene block copolymers (S-I-S) and styrene-butadiene-styrene block copolymers (S-B-S) are widely used in these adhesive compositions. Both classes of block copolymers give the adhesive compositions specific properties related to the respective inherent characteristics of these block copolymers.
For example, the softness of S-I-S makes this polymer type the material of choice for pressure sensitive applications in tapes and labels, while the elevated cohesion of S-B-S makes this material attractive for construction adhesives for disposable soft goods.
S-I-S block copolymers have until now successfully been applied in industrial and packaging tape and label applications.
More in particular, from e.g. U.S. Pat. No. 5,389,438 (MINNESOTA MINING MFG) 02.12.1995; EP 306232 A (MINNESOTA MINING MFG) 08.03.1989; EP 443263 A (MINNESOTA MINING MFG) 28.08.1991; WO 0014170 (EXXON) 16.03.2000 and U.S. Pat. No. 6,384,138 (EXXON) 07.05.2002 adhesive compositions to be used for tapes, labels, bandages or disposable sanitary articles, such as diapers and incontinence garments, were known. Said adhesive compositions comprised:    1. at least one block copolymer, comprising at least two terminal blocks of poly(vinyl aromatic compound) and at least one midblock of poly(isoprene) or poly(butadiene) or poly(ethylene-butylene), i.e. hydrogenated poly(butadiene, or a mixture of said block copolymers,    2. at least one tackifying resin, and    3. a plasticizer.
It will be appreciated that in none of said publications any reference is made to the use of the adhesive compositions at low temperatures, i.e. below room temperature.
Although in particular S-I-S block copolymer containing compositions showed outstanding tack, peel and cohesion at room temperature, i.e. at temperatures around 20° C., they have appeared to lack adequate adhesive properties in cold environments, namely 5° C. and below.
It is well known from e.g. Handbook of Pressure Sensitive Adhesive Technology, Don Satas, Chapter 13, Thermoplastic Rubbers, A-B-A block copolymers, p 367 (1989, 2nd ed.), that most adhesive compositions based on S-I-S block copolymers loose their tack and adhesion properties as temperature decreases from about 15° C.
It was possible to formulate adhesive compositions based on S-I-S block copolymers, having a good tack below 15° C., but in order to achieve an acceptable compromise with the adhesive properties, relatively low proportions of high softening point hydrocarbon resins and relatively high proportions of plasticizers are needed.
However, high proportions of plasticizer have the disadvantages (a) that the peel and cohesion of the adhesive is reduced and (b) that the plasticizer migrates out of the formulation, modifying the visual and property appearance of the final products, like oily spots in a paper label.
During the splitting of roll products, too much oil generates edge oozing, provoking that two adjacent rolls stick together.
Therefore there is a strong need for adhesive compositions which keep good tack, adhesion and cohesion at low temperatures, and more in particular at temperatures in the range from +5 to −25° C., which enables the manufacture of tapes and labels to be used in cold environments e.g. some electrical insulating tapes or on frozen articles, e.g. food and medicines in deep freezers.
It is an object of the present invention to provide adhesive compositions which keep good tack, adhesion and cohesion at low temperatures, and which do not contain high amounts of plasticizers.
Another object of the present invention is formed by labels and tapes which retain adequate properties when stored for a long time at low temperatures.
Another object of the present invention is to provide adhesive compositions which enable the manufacture of repositionable or removable tapes, labels and bandages (e.g. plasters) which can be used at low temperatures.
As result of extensive research and experimentation, said adhesive compositions aimed at, and labels, tapes and bandages to be manufactured from them, have now surprisingly been found.